Cell measurement and special function small cell selection method and apparatus for use in a mobile communication system

ABSTRACT

Disclosed is a method by a base station in a wireless communication system. The method includes receiving cell measurement information related to the serving and neighboring cells from at least one terminal served by the base station, receiving status information including load information on serving cells of the small cell base station from the small cell base station, determining a secondary cell group (SCG) of the serving cells of the small cell base station that are capable of serving the terminal based on the cell measurement information and the status information and transmitting information on the SCG to the small cell base station.

CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

The present application is a continuation of U.S. patent applicationSer. No. 14/663,673 filed Mar. 20, 2015, which is related to and claimsthe benefit under 35 U.S.C. §119(a) of a Korean patent application filedin the Korean Intellectual Property Office on Mar. 21, 2014 assignedSerial No. 10-2014-0033233, all of which are incorporated herein byreference into the present disclosure as if fully set forth herein.

TECHNICAL FIELD

The present disclosure relates to a cell measurement and specialfunction cell selection method and apparatus for use in a mobilecommunication system. In particular, the present disclosure relates to amethod and apparatus for selecting pSCell among the small cells of themobile communication system.

BACKGROUND

Mobile communication systems were developed to provide mobile users withcommunication services. With the rapid advance of technologies, themobile communication systems have evolved to the level capable ofproviding high speed data communication services beyond the earlyvoice-oriented services. Recent studies are focused on the LTE-Advanced(LTE-A) for improving data rates with the adoption of various newtechniques to the legacy LTE system. The LTE-A standardization is almostcompleted to the extent of commercialization around late 2010, therecent studies are focused on the improvement of data rates with theadoption of various technologies.

One of the representative technologies for increasing the data rate isDual Connectivity. The Dual Connectivity is a technology for a terminalto transmit/receive data to and from a plurality of base stations inparallel. In order to accomplish this, it is necessary for the terminalto monitor the cells continuously to check the signals rich enough forconnection through efficient operations without increasing thecomplexities of the terminal and network.

SUMMARY

To address the above-discussed deficiencies, it is a primary object ofthis disclosure to provide a cell measurement and special function cellselection method and apparatus for use in a mobile communication system.The present disclosure provides a cell measurement and special functioncell selection method and apparatus that is capable of managing servingcells efficiently in the mobile communication system supporting dualconnectivity.

In accordance with the present disclosure, a method implemented by abase station in a wireless communication system is provided. The methodcomprises receiving cell measurement information related to the servingand neighboring cells from at least one terminal served by the basestation, receiving status information including load information onserving cells of the small cell base station from the small cell basestation, determining a secondary cell group (SCG) of the serving cellsof the small cell base station that are capable of serving the terminalbased on the cell measurement information and the status information andtransmitting information on the SCG to the small cell base station.

In accordance with the present disclosure, a base station in a wirelesscommunication system is provided. The base station comprises atransceiver configured to transmit and receive a signal and a controllerconfigured to receive cell measurement information related to theserving and neighboring cells from at least one terminal served by thebase station, to receive status information including load informationon serving cells of the small cell base station from the small cell basestation, to determine a secondary cell group (SCG) of the serving cellsof the small cell base station that are capable of serving the terminalbased on the cell measurement information and the status information,and to transmit information on the SCG to the small cell base station.

In accordance with the present disclosure, a small cell base station ina wireless communication system is provided. The small cell base stationcomprises a transceiver configured to transmit and receive a signal anda controller configured to receive information on a secondary cell group(SCG) of the small cell base station that are capable of serving theterminal from a base station, and select a specific cell for a physicaluplink control channel (PUCCH) of the terminal based on the informationon the SCG.

In accordance with the present disclosure, a method implemented by asmall cell base station in a wireless communication system is provided.The method comprises receiving information on a secondary cell group(SCG) of the small cell base station that are capable of serving theterminal from a base station, and selecting a specific cell for aphysical uplink control channel (PUCCH) of the terminal based on theinformation on the SCG.

In accordance with the present disclosure, a terminal in a wirelesscommunication system is provided. The terminal comprises a transceiverconfigured to transmit and receive a signal; and a controller configuredto receive small cell base station configuration information includingan indicator indicating the specific cell from a base station, andtransmit a physical uplink control channel (PUCCH) to a small cell basestation via the specific cell indicated by the indicator. The specificcell is determined based on a secondary cell group (SCG) of servingcells of the small cell base station that are capable of serving theterminal, and the SCG is determined based on cell measurementinformation measured by the terminal and the status information of thesmall cell base station.

In accordance with the present disclosure, a method implemented by aterminal in a wireless communication system is provided. The methodcomprises receiving small cell base station configuration informationincluding an indicator indicating the specific cell from a base stationand transmitting a physical uplink control channel (PUCCH) to a smallcell base station via the specific cell indicated by the indicator. Thespecific cell is determined based on a secondary cell group (SCG) ofserving cells of the small cell base station that are capable of servingthe terminal, and the SCG is determined based on cell measurementinformation measured by the terminal and the status information of thesmall cell base station.

The cell measurement and special function cell selection method andapparatus of the present disclosure is advantageous in terms of managinga plurality of small cells efficiently in a mobile communication system.

Also, the cell measurement and special function cell selection methodand apparatus is advantageous in that a SeNB selects a special cellefficiently in the mobile communication system supporting the dualconnectivity.

Also, the cell measurement and special function cell selection methodand apparatus is advantageous in that the MeNB selects a special cellefficiently in the mobile communication system supporting the dualconnectivity.

Furthermore, the cell measurement and special function cell selectionmethod and apparatus is advantageous in terms of reducing powerconsumption of the terminal in the mobile communication systemsupporting the dual connectivity and carrier aggregation.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates a Dual Connectivity of LTE according to thisdisclosure;

FIG. 2 illustrates an operation between a user equipment (UE) and eNBsfor configuring a secondary cell group (SCG) and specific candidate setaccording to embodiments of the present disclosure;

FIG. 3 is a table listing the events triggering cell measurement reportsto the eNB according to embodiments of the present disclosure;

FIG. 4 illustrates a signal flow diagram of a PCell selection procedurebased on the option 1 according to embodiments of the presentdisclosure;

FIG. 5 illustrates a signal flow diagram of a PCell change procedurebased on the option 1 according to embodiments of the presentdisclosure;

FIG. 6 illustrates a signal flow diagram of a pSCell selection procedurebased on the option 2 according to embodiments of the presentdisclosure;

FIG. 7 illustrates a signal flow diagram of a pSCell selection procedurebased on the option 3 according to embodiments of the presentdisclosure;

FIG. 8 illustrates a signal flow diagram of a pSCell procedure based onthe option 4 according to embodiments of the present disclosure;

FIG. 9 illustrates a signal flow diagram of a procedure of deliveringthe pSCell information to the UE according to embodiments of the presentdisclosure;

FIG. 10 illustrates a signal flow diagram of a pSCell informationnotification procedure of the MeNB according to embodiments of thepresent disclosure;

FIG. 11 illustrates a signal flow diagram of a procedure of applyingS-Measure according to a LTE standard technical specification;

FIG. 12 illustrates a diagram for explaining the S-measure specified inthe LTE standard technical specification;

FIG. 13 illustrates a diagram for explaining the problem likely to occurin applying the S-Measure to the dual connectivity or carrieraggregation technique;

FIG. 14 illustrates a signal flow diagram of a procedure of ignoringS-Measure in association with a predetermined technique according toembodiments of the present disclosure;

FIG. 15 illustrates cell measurement for reducing power consumption of aUE operating in the dual connectivity or carrier aggregation modeaccording to embodiments of the present disclosure;

FIG. 16 illustrates the UE-side operation of the cell measurementprocedure for reducing the power consumption of the UE operating in thedual connectivity or carrier aggregation mode according to embodimentsof the present disclosure;

FIG. 17 illustrates a configuration of the UE according to embodimentsof the present disclosure; and

FIG. 18 illustrates a configuration of the eNB according to embodimentsof the present disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 18, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless communication system.Embodiments of the present disclosure are described with reference tothe accompanying drawings in detail. The same reference numbers are usedthroughout the drawings to refer to the same or like parts. Detaileddescription of well-known functions and structures incorporated hereinmay be omitted to avoid obscuring the subject matter of the presentdisclosure. This aims to omit unnecessary description so as to make thesubject matter of the present disclosure clear.

The present disclosure provides an efficient cell measurement andspecial function cell selection method and apparatus that is capable ofmanaging serving cells efficiently in a mobile communication systemsupporting parallel connections to multiple base stations (e.g. dualconnectivity system).

If the terminal is capable of communicating with multiple base stationssimultaneously, it is possible to increase the data rate per terminal.In the LTE standard, this topic is discussed under the title of ‘dualconnectivity.’ The present disclosure proposes a cell measurement andserving cell management method inevitable for implementation of dualconnectivity.

A brief description is made of the concept of the dual connectivityunder discussion in the LTE standardization process before beginning theexplanation of the present disclosure.

FIG. 1 illustrates Dual Connectivity of LTE according to thisdisclosure. Referring to FIG. 1, a User Equipment (UE) 105 maintainsconnectivity to a macro evolved Node B (eNB) 100 and a small cell eNB110 simultaneously for data transmission/reception. The macro eNB 100 isreferred to as Master eNB (MeNB), and the small cell eNB 110 asSecondary eNB (SeNB). A plurality of small cells are located within theservice area of the MeNB 100 which is connected to the SeNBs throughwired backhaul networks.

It is assumed that the UE 105 uses total 5 serving cells belonging tothe MeNB 100 and the SeNB 110. The set of serving cells of the MeNB 100is referred to as Master Cell group (MCG) 120, and the MCG has onePrimary Cell (PCell) 125 controls the functions of a legacy normal cell,such as connection establishment, connection re-establishment, andhandover. The PCell 125 has a Physical Uplink Control Channel (PUCCH).The other serving cell(s), with the exception of the PCell 125, isreferred to as Secondary Cell (SCell) 130.

FIG. 1 is directed to a scenario in which the MeNB 100 has one SCell 130and the SeNB 110 has three SCells. The set of serving cells of the SeNB110 is referred to as Secondary Cell Group (SCG) 140. In the course oftransmitting/receiving data to/from the two eNBs, the MeNB 100 maygenerate a command to the SeNB 110 for adding, modifying, or releasing aserving cell. For this purpose, the MeNB 100 may send serving cell andneighbor cell measurement configuration information to the UE 105. TheUE 105 performs measurement and report the measurement result to theMeNB 100 according to the configuration information.

In order for the SeNB 110 to transmit/receive data to/from the UE 105, aserving cell acts in a similar role as the PCell 125 of the MCG 120. Inthe present disclosure, such a cell is referred to as primary SCell(pSCell). The pSCell is one of the serving cells of the SCG 140 and hasa PUCCH. The PUCCH carries Hybrid Automatic Repeat RequestAcknowledgement/Negative-Acknowledgement (HARQ ACK/NACK), Channel StatusInformation (CSI), and Scheduling Request (SR).

The present disclosure proposes a cell measurement method that iscapable of allowing the MeNB 100 to configure the SCG 140 efficiently.Also, the present disclosure provides a method of selecting the pSCell.Also, the present disclosure provides a method of conserving powerconsumption of the UE in the dual connectivity mode.

Embodiment 1

This embodiment provides an efficient cell measurement method and apSCell selection method in the dual connectivity mode. The pSCellselection method can be summarized as follows.

Option 1) The SeNB selects one of the cells of the SCG indicated by theMeNB.

Option 2) The SeNB selects one of the cells of a specific candidate setindicated by the MeNB.

Option 3) The MeNB selects one of the cells of the SCG which the MeNBindicates to the SeNB.

Option 4) The MeNB selects one of the cells of a specific candidate setwhich the MeNB indicates to the SeNB.

FIG. 2 illustrates operation between a UE and eNBs for configuring anSCG and specific candidate set according to embodiments of the presentdisclosure. Referring to FIG. 2, the MeNB 200 receives SeNB statusinfoiivation from the SeNB 265 as denoted by reference number 255. Thestatus information includes the information on the loads of the servingcells of the SeNB 265 in use. The MeNB 200 may send the UE 285 themeasurement configuration in order for the UE 285 to measure the servingand neighboring cells and report the measurement result as denoted byreference number 270. The UE 285 performs measurement as denoted byreference number 280 and reports the measurement result to the MeNB 200periodically or when a predetermined condition is fulfilled as denotedby reference number 275. In the legacy LTE standard, the UE reports thecell measurement result to the eNB when a predetermined condition isfulfilled.

FIG. 3 is a table listing the events triggering cell measurement reportsto the eNB according to embodiments of the present disclosure. Referringto FIG. 3, each event is defined in association with a predeterminedcondition. If the measurement result fulfills the condition, the UEreports the corresponding measurement result to the eNB. Each conditionis divided into an entering condition and a leaving condition. Theentering condition corresponds to triggering the event, and the leavingcondition corresponds to no longer triggering the event. The differencebetween the two conditions is the difference between a value obtained bysubtracting a predetermined hysteresis value from a threshold value anda value obtained by adding the hysteresis value to the threshold value.This is for preventing the event from occurring to frequently in theradio environment varying abruptly in a small area as time goes.

For all the events, when the entering condition is fulfilled, the UEreports the cell measurement information to the eNB. In the case of theEvent A3/A6, the UE reports the cell measurement information to the eNBeven when the leaving condition is fulfilled. The MeNB determines theSCG cell 220 based on the status information provided by the SeNB 265and the cell measurement value reported by the UE. The MeNB 200determines to use its two cells (i.e. the PCell 210 and the SCell 215)and three serving cells 225, 230, and 235 of the SeNB 265. The MeNB 200configures or updates the SCG of the SeNB 265 by commanding the SeNB 265to add, modify, or release an SCG cell as denoted by reference number260.

In the Options 2 to 4, the MeNB 200 may configure a pSCell candidate set240. The cells included in the candidate set 240 have to be included atleast in the SCG 220. That is, the candidate set 240 is a subset of theSCG 220. In FIG. 2, the two serving cells 245 and 250 of the SCG 220 areincluded in the candidate set 240. The candidate set 240 may becomprised of the cells with good signal strengths among the SCG cells.This is because the pSCell has to perform more functions than other SCGcells and because if the pSCell has good signal strength, this is likelyto be advantageous in various aspects. For example, if the pSCell haslow transmission/reception error probability as compared to other SCGcells, it is likely to increase the probability for the UE to succeedthe transmission of the control signal on the PUCCH of the pSCell.Throughout transmission/reception performance of the SCG cell ismaintained above a predetermined level.

In embodiments of the present disclosure, the MeNB 200 notifies the SeNB265 of a set of the cells fulfilling a predetermined condition among thecells of the SCG 220 such that the SeNB 265 selects the pSCell inconsideration of predetermined supplementary information. The set(candidate set) is a subset of the SCG 220. The predetermined conditionmay be whether the received signal quality (e.g. Reference SignalReceived Power (RSRP) or Reference Signal Received Quality (RSRQ)) isgreater than a predetermined threshold value. If the candidate set 240is identical with the SCG 220, the MeNB 200 may not inform the SeNB 265of the candidate set 240 explicitly. That is, if the pSCell candidateset is identical with the SCG 220, the process in which the MeNB 200notifies the pSCell candidate set of the SeNB may be omitted. Inembodiments of the present disclosure, the SeNB 265 determines thepSCell in the candidate set based on at least one of: a per-cell load, atraffic amount, an available radio resource amount, and CQI.

Descriptions are made of the per-option operations in detailhereinafter. Option 1 is that the SeNB selects one of the SCG cellsindicated by the MeNB.

FIG. 4 illustrates a signal flow diagram of a PCell selection procedurebased on the option 1 according to embodiments of the presentdisclosure. Referring to FIG. 4, the MeNB 405 collects predeterminedinformation from the UE 400 and the SeNB 410 to determine a SecondaryCell Group (SCG). The MeNB 405 requests the UE 400 for serving andneighbor cells measurement information and the SeNB 410 for SeNB statusinformation as denoted by reference number 415. The MeNB 405 sends cellmeasurement configuration information to the UE 400 using a RadioResource Control (RRC) Connection Reconfiguration(RRCConnectionReconfiguration) message at step 420. The UE 400 performscell measurement according to the configuration information at step 430.The UE 400 reports the measurement result to the MeNB 405 periodicallyor in an event-triggered manner using a Measurement Report message atstep 435.

Meanwhile, the SeNB 410 continuously monitors the SCG cells to collectthe SeNB status information at step 425. The SeNB status informationincludes cell load information and current radio resource use amount.The SeNB status information is sent to the MeNB 405 at step 440. TheMeNB 400 determines the SCG cells of the SeNB 410 for use in servicebased on the information collected from the UE 400 and the SeNB 410 atstep 445.

In order to determine the SCG cells at a suitable timing, the UE 400reports the cell measurement report to the MeNB 405 when a predeterminedevent occurs. Typically, the MeNB 405 may use legacy measurement eventsto configure the SCG cells. For example, Event A4 from Table 3 may beused for adding a new serving cell, Event A2 for releasing a cell fromthe SCG, and Event A6 for supporting inter-frequency SCG mobility. Thatis, the MeNB 405 may configure Event A4 to the UE 400 and thus, if thereis any cell fulfilling a condition associated with a predeterminedthreshold value among the neighboring cells, the UE 400 reports the cellmeasurement result to the MeNB 405. The MeNB 405 may determine to addthe cell fulfilling the condition associated with the threshold value tothe SCG in consideration of additional information. The MeNB 405commands the SeNB 410 to add the cell to the SCG at step 450.

In Option 1, the SeNB 410 determines the pSCell. The SeNB 410 determinesone of the SCG cells informed by the MeNB 405 as the pSCell according toa predetermined rule. At this time, the SeNB 410 may select a fewcandidate cells fulfilling a predetermined condition among the SCG cellsat step 455 and then determine one of the candidate cells as the PCellat step 460. It is also possible for the SeNB 410 to select one of theall SCG cells as the pSCell.

In order to select one of the SCG cells, the SeNB 410 may use varioussupplementary information. It is a simple method to select one of theSCG cells randomly. However, the random selection is inefficient. Inorder to select the pSCell more efficiently, the SeNB 410 may considerthe cell loads of the respective SCG cells. It is not preferably toselect the cell with a high load condition and radio resource shortage.The SCG cell with relatively good signal strength can be selected as thepSCell.

In order to achieve this, the SeNB 410 has to know the received signalqualities of the respective SCG cells. The SeNB 410 may receive thereceived signal quality informations of the SCG cells from the MeNB 405or collect the informations by itself. In the case that the receivedsignal quality informations are provided by the MeNB 405, theinformations may be reported by the UE. A received signal qualityinformation may be the RSRP or RSRQ of each SCG cell. However, if theMeNB 405 provides the SeNB 410 with the received signal qualityinformation, this increases the information exchange traffic between theMeNB 405 and the SeNB 410.

The SeNB 410 may collect the received signal equality information of theSCG cells by itself. It is impossible for the SeNB 410 to receive thecell measurement result from the UE. This is because, in the LTEstandard, the UE 400 in the dual connectivity mode can report the cellmeasurement result to only the MeNB 405. However, the UE may provide theSeNB 410 with other information that can be used for estimating thereceived signal quality. A representative one of such information isChannel Quality Indicator (CQI). The CQI indicates a data rate that theUE 400 supports in downlink. That is, if the CQI indicates a high datarate, this means that the downlink signal quality is good.

According to embodiments of the present disclosure, the SeNB 410 selectsone of the cells belonging to an SCG from a predetermined candidate setas the pSCell based on the cell loads of the SCG cells or CQI. If thepSCell is determined, the SeNB 410 notifies the UE 400 of the pSCell viathe MeNB 405 as denoted by reference number 480. The SeNB 410 sends, tothe MeNB 405, the SeNB configuration information including the pSCellinformation at step 465. The pSCell remains in the activated state atstep 475. The MeNB 405 sends the UE 400 an RRC ConnectionReconfiguration (RRCConnectionReconfiguration) message including thepSCell information at step 470. The PCell information is described inmore detail below. The UE 400 sends the SeNB 410 the control informationon the PUCCH of the pSCell.

FIG. 5 illustrates a signal flow diagram of a PCell change procedurebased on the option 1 according to embodiments of the presentdisclosure. In the embodiment of FIG. 5, in step 515, the UE 500, MeNB505, and SeNB 510 operate as described in the process 415 of FIG. 4. TheMeNB 505 determines whether it is necessary to update the SCG of theSeNB 510 in use at step 520. For example, if a certain cell of the SCGdoes not fulfill the minimum signal strength requirement or if the cellload of the SeNB 510 drops and thus SCG cells are redundant, the MeNB505 may determine to release some SCG cells. If is the MeNB 505determines to update the SCG, the MeNB 505 adds or releases at least onecell to or from the SCG at step 525. The SeNB 510 updates the SCG anddetermines whether the released cell is the pSCell at step 530. If thereleased cell is the pSCell, the SeNB 510 selects a new SCG cell as thepSCell at step 535. The SeNB 510 notifies the UE 500 of the newlyselected pSCell via the MeNB 505 at step 540.

FIG. 6 illustrates a signal flow diagram of a pSCell selection procedurebased on the option 2 according to embodiments of the presentdisclosure. Referring to FIG. 6, in step 615, the UE 600, MeNB 605, andSeNB 610 operate as described in the process 415 of FIG. 4. The MeNB 605configures a SCG composed of the cells of the SeNB 610 at step 620. TheMeNB 605 determines a pSCell candidate set composed of the cellsbelonging to the SCG at step 625. That is, the candidate set is a subsetof the SCG. The MeNB 650 may configure the candidate set with the cellshaving good signal strengths among the SCG cells.

In order to configure the candidate set, the UE 600 reports the cellmeasurement result to the MeNB 605 in an event-triggered manner. Supposethat the MeNB 605 configures the candidate set with the serving cellsfulfilling a predetermined received signal quality condition among theSCG cells. The received signal quality threshold value for determiningthe candidate cell may be higher than the threshold value fordetermining the SCG cell.

In order to maintain the candidate set, the UE reports the cellmeasurement result to the MeNB whenever detecting a serving cell thatfulfills the received signal quality condition for candidate or does notfulfill the conditions any longer. For this purpose, it is necessary tocheck whether the measurement event of the legacy LTE standard can beused. One method is to configure Events A1 and A2 with thresholds, whichdiffer from those for the legacy use, to the UE. This means to configureEvents A1 and A2 with thresholds for use in candidate set management inaddition to Events A1 and A2 for use in SCG management purpose. However,this method has a shortcoming in that the cell measurement configurationinformation transmitted from the eNB to the UE increases.

Another method is for the UE 600 to report the cell measurement resultto the eNB when a leaving condition is fulfilled in association withEvent A1. This is advantageous in that the configuration informationdoes not increase. It is also possible to use the status informationprovided by the SeNB 610 additionally. The MeNB 605 sends, to the SeNB610, the SCG information and the candidate set information generated asabove at step 630. The SeNB 610 determines one of the cells included inthe candidate set as the pSCell at step 635. As described above, theSeNB 610 determines the pSCell based on the cell load, available radioresource amount, and scheduling information on the current servingcells. The SeNB 610 sends the UE 600 the PCell information via the MeNB605 at step 640.

The pSCell is selected among the serving cells of the SCG and has PUCCH.The PUCCH carries HARQ ACK/NACK, CSI, and SR that are transmitted fromthe UE to the eNB. It does not prefer to change the pSCell in view ofsystem management. If the pSCell is changed frequently, trafficincreases between the UE and the eNB, resulting in network overload.According to embodiments of the present disclosure, options 2 and 4 arecharacterized by configuration of a candidate set for selecting thepSCell so as to mitigate the aforementioned problem.

In the case of option 2 where the SeNB 610 selects the pSCell by itself,it is necessary to acquire the cell measurement informations of therespective SCells of the eNB. Since the UE 600 does not provide the SeNBthe cell measurement information, the SeNB receives the cell measurementinformation from the MeNB 506, and this increases network load.According to embodiments of the present disclosure, the MeNB 605configures the candidate set based on the cell measurement informationprovided by the UE 600 and notifies the SeNB of this such that the SeNBcan select the pSCell from the candidate set composed of the cells ofwhich signal strengths are equal to or greater than a predeterminedthreshold without receipt of extra cell measurement information from theMeNB.

If the candidate set information is received, the SeNB 610 may use thecandidate set depending on the case. If the MeNB 605 updates thecandidate set, the candidate set which is stored in the MeNB 605 orwhich has been transmitted to the SeNB 610 is not used for selecting thepSCell. Although there is no update of the candidate set, if an eventtriggering the change of the pSCell of the SeNB, the SeNB 610 may selectone of the SCells belonging to the candidate set stored or receivedpreviously as a new pSCell. That is, when a pSCell change event occurs,the SeNB 610 may perform pSCell reselection in the candidate set storedor received previously without performing the entire process forselecting the pSCell unless the candidate set is changed. In this way,it is possible to reduce the traffic load of the network.

FIG. 7 illustrates a signal flow diagram of a pSCell selection procedurebased on the option 3 according to embodiments of the presentdisclosure. Referring to FIG. 7, in step 715, the UE 700, MeNB 705, andSeNB 710 operate as described in the process 415 of FIG. 4. The MeNB 705configures an SCG composed of the cells of the SeNB 710 at step 720. TheMeNB 705 determines one of the cells of the SCG as the pSCell at step725. In order to determine the pSCell, the MeNB 705 has to have the allthe informations necessary for pSCell determination.

The MeNB 705 notifies the SeNB 710 of the SCG and pSCell at step 730.The SeNB 710 generates the SeNB configuration information includingpSCell indicator and information on the PCell and sends the generatedinformation to the UE 700 via the MeNB 705 at step 735. Since the MeNB705 determines the pSCell, it is possible for the MeNB 705 to generatethe pSCell information and send the pSCell information to the UE 700.However, other pSCell-related information is still generated by the SeNB710.

FIG. 8 illustrates a signal flow diagram of a pSCell procedure based onthe option 4 according to embodiments of the present disclosure.Referring to FIG. 8, the UE 800, MeNB 805, and SeNB 810 operate asdescribed in the process 415 of FIG. 4 at step 815. The MeNB 805configures an SCG composed of the cells of the SeNB 810 at step 820. TheMeNB 805 determines a pSCell candidate set of SCG cells at step 825. Thecandidate set may be determined as described with reference to FIG. 6.The MeNB 805 determines one of the SCG cells of the candidate set as thepSCell at step 830. The MeNB 805 notifies the SeNB 810 of the SCG andthe pSCell at step 835. The SeNB 810 generates the pSCell information,which is transmitted to the UE 800 via the MeNB 805 at step 840. This issimilar to step 735 of FIG. 7.

FIG. 9 illustrates a signal flow diagram illustrating a procedure ofdelivering the pSCell information to the UE according to embodiments ofthe present disclosure. Referring to FIG. 9, when the SeNB 910determines the pSCell according to option 1 or option 2, any pSCellindication information has to be included in the SeNB configurationinformation which is transmitted from the SeNB 910 to the MeNB 905 atstep 915. This process is valid either in option 3 or option 4. One ofthe main characteristics of the pSCell is that it has PUCCH.Accordingly, the SeNB configuration information may include the pSCellPUCCH configuration information (PUCCH-Config IE). The MeNB 905 sendsthe UE 900 a RRC Connection Reconfiguration(RRCConnectionReconfiguration) message including this information atstep 920. It is important to notify the UE 900 of which is the pSCellamong the SCG cells. This embodiment is characterized in that one of thefollowing informations is used to indicate the pSCell.

-   -   CellGlobalId (CGI): Unique cell ID. The CGI is comprised of PLMN        ID, eNB ID, and Cell ID. Identical with the IE specified in 3GPP        standard TS36.331.    -   PhysCellId (PCI): This is an ID identifying the physical layer        of a cell and can be reused in other cells. Identical with the        IE specified in 3GPP standard TS36.331.    -   SCellIndex (or ServCellIndex)-based: Since the pSCell is one of        SCells, it is allocated an SCellIndex value for use in SCell        identification. The SCellIndex is an integer value in the range        from 1 to 7. The eNB uses the SCellIndex of the pSCell to notify        the UE of the pSCell. For example, if the SCellIndex of the        pSCell is set to 2, the Information Element (IE) which is newly        defined to indicate pSCell has the value of 2. This IE is        included in the RRCConnectionReconfiguration message transmitted        at step 920.    -   1-bit indicator within each SCell configuration: The eNB        provides the UE with per-SCell configuration information. The        1-bit indicator is defined in the per-SCell configuration        information and set to TRUE for indicating a SCell as the        pSCell. For example, this indicator may be included in the        SCellToAddMod IE.    -   Bitmap: A bitmap mapping SCells to bits in order is defined such        that the bit corresponding to the pSCell is set to 1.

FIG. 10 illustrates a signal flow diagram of a pSCell informationnotification procedure of the MeNB according to embodiments of thepresent disclosure. Referring to FIG. 10, the MeNB 1005 determines thepSCell based on the option 3 or 4 and notifies the UE 1000 that whichSCG cell is the pSCell. The SeNB 1010 sends the MeNB 1005 the SeNBconfiguration information at step 1015. Although the pSCell is notdetermined by the SeNB 1010, the SeNB 1010 has to configure the PUCCH ofthe pSCell. The SeNB configuration information includes the pSCell PUCCHconfiguration information. The MeNB 1005 generates the RRC ConnectionReconfiguration (RRCConnectionReconfiguration) message including theSeNB configuration information and the pSCell indication information1020 and transmits the RRC Connection Reconfiguration message to the UE1000 at step 1025.

Embodiment 2

This embodiment proposes a method for conserving power consumption ofthe UE in the carrier aggregation or dual connectivity mode usingmultiple serving cells. In order to save the power consumption of the UEin the connected mode, which is configured to perform cell measurement,the UE performs cell measurement only when a predetermined condition isfulfilled other than continuously. If S-Measure IE is included in thecell measurement configuration information, the UE performsintra-frequency, inter-frequency, and/or inter-RAT measurement only whenthe Reference Signal Received Power (RSRP) of the PCell is less than thevalue indicated by the S-Measure.

FIG. 11 illustrates a signal flow diagram of a procedure of applyingS-Measure in LTE standard technical specification. Referring to FIG. 11,the MeNB 1105 sends the UE 1100 the cell measurement configurationinformation including the S-Measure using the RRC ConnectionReconfiguration (RRCConnectionReconfiguration) message at step 1110. TheUE 1100 determines whether the RSRP of the PCell is less than the valueindicated by the S-Measure at step 1115. If the RARP of the PCell isless than the value indicated by the S-Measure, the UE 1100 performsintra-frequency, inter-frequency, and inter-RAT measurements at step1115. If the RARP of the PCell is equal to or greater than the valueindicated by the S-Measure, the UE 1100 does not perform and y ofintra-frequency, inter-frequency, and inter-RAT measurements. In thiscase, the UE 1100 performs just the serving measurement.

FIG. 12 illustrates a diagram for explaining the S-measure specified inthe LTE standard technical specification. Referring to FIG. 12, if theRSRP 1200 of the PCell is greater than the value 1205 indicated by theS-Measure, the UE performs only the serving cell measurement as denotedby reference number 1210. Otherwise if the RSRP is equal to or less thanthe value indicated by the S-Measure, the UE performs intra-frequency,inter-frequency, and inter-RAT measurements as denoted by referencenumber 1215.

In the case that only the PCell exists, if the RSRP of the PCell isgood, there is no need for cell measurement result for handover. In thiscase, the UE may skip unnecessary cell measurement to save powerconsumption of the UE. However, there is a problem in that it isdifficult to apply the S-Measure to the dual connectivity technique orthe carrier aggregation technique in which multiple serving cells areparticipating.

FIG. 13 illustrates a diagram for explaining the problem likely to occurin applying the S-Measure to the dual connectivity or carrieraggregation technique. For example, the UE transmits/receives datathrough the PCell and SCell in FIG. 13. The RSRP 1300 of the PCell isgreater than the S-Measure 1305. However, the RSRP 1310 of the SCell isless than the S-Measure 1305 and has poor signal strength. In this case,it is necessary to change the SCell for new serving cell.

In order to change the SCell, the UE performs intra-frequencymeasurement as denoted by reference number 1320 and reports theneighboring cell measurement result to the eNB. However, since the RSRPof the PCell is greater than S-Measure, the UE performs only the servingcell measurement. Accordingly, although the signal strength of the SCelldrops below a predetermined threshold value so as to trigger Event A2 toreport the measurement report, the measurement result of the suitableneighboring cell is not likely to be included. The present disclosureprovides a method for solving such a problem. The simplest method is toignore the S-measurement when a specific technique is running. If theS-Measure is ignored, this means that the UE may perform intra-frequencymeasurement according to the RSRP of the SCell even when the RSRP of thePCell is greater than the S-measure. The UE also may performinter-frequency and inter-RAT measurements.

FIG. 14 illustrates a signal flow diagram of a procedure of ignoringS-Measure in association with a predetermined technique according toembodiments of the present disclosure. Referring to FIG. 14, the MeNB1405 sends, to the UE 1400, the RRC Connection Reconfiguration(RRCConnectionReconfiguration) message including the S-Measure at step1410. The UE 1400 determines whether the UE 1400 is operating in thedual connectivity mode or the carrier aggregation mode at step 1415. Ifthe dual connectivity mode or the carrier aggregation mode is activated,the UE 1400 ignores the S-Measure regardless of the received signalquality of the PCell at step 1420. That is, the UE 1400 may performintra-frequency measurement even when the RSRP of the PCell is greaterthan the S-Measure. However, this method negates the change of savingthe power consumption of the UE too. The present disclosure provides amethod for the UE to perform: when a predetermined condition isfulfilled, at least the intra-frequency measurement can support SCellmobility.

FIG. 15 illustrates cell measurement for reducing power consumption ofthe UE operating in the dual connectivity or carrier aggregation modeaccording to embodiments of the present disclosure. The eNB provides theUE with two threshold values. One is the S-Measure 1500 specified in thelegacy LTE standard. The other is a new threshold value 1510 to becompared with the RSRP of the SCell. This new threshold is referred toas S-MeasureForScell 1510 in the present invention. The legacyS-Measure-related operation is performed without modification. That is,if the PCell RSRP is less than the S-Measure, the UE performsintra-frequency, inter-frequency, and inter-RAT measurements as denotedby reference number 1525.

Even when another condition is fulfilled, the UE may perform theintra-frequency, inter-frequency, and inter-RAT measurements. If theSCell RSRP is less than the S-MeasureForScell, the UE may perform atleast intra-frequency measurement. The inter-frequency and inter-RATmeasurements may be included. Since it is to change the SCell with thepoor signal strength for a neighboring cell on the same frequency, it isinevitable to perforin the intra-frequency measurement. In the case thatthere is a plurality SCells, if the RSRP of at least SCell is less thanthe S-MeasureForSCell 1510, the UE performs the cell measurement.

FIG. 16 illustrates a flowchart of the UE-side operation of the cellmeasurement procedure for saving the power consumption of the UEoperating in the dual connectivity or carrier aggregation mode accordingto embodiments of the present disclosure. Referring to FIG. 16, the MeNBsends the UE the cell measurement configuration information includingthe S-Measure and S-MeasureForSCell using the RRC ConnectionReconfiguration (RRCConnectionReconfiguration) message. The MeNB maytransmit the cell measurement configuration information including onlythe S-Measurement or both the S-Measure and S-MeasureForSCell to the UEusing the RRC Connection Reconfiguration information. The MeNB also maytransmit the cell measurement configuration information includingneither the S-Measure nor the S-MeasureForSCell using the RRC ConnectionReconfiguration message. The UE determines whether the cell measurementconfiguration information received from the eNB includes the S-Measureat step 1600. That is, the UE determines whether the cell measurementconfiguration information includes only the S-Measure, both theS-Measure and S-MeasureForSCell, or none of the S-Measure andS-MeasureForSCell at step 1600.

If both the cell measurement configuration information includes both theS-Measure and S-MeasureForSCell, the UE determines whether either thePCell RSRP is less than the S-Measure or the SCell RSRP is less than theS-MeasureForSCell at step 1605 and, if so, the UE performsintra-frequency, inter-frequency, and inter-RAT measurements at step1610. One of the conditions is related to the operation of the S-Measurespecified in the legacy LTE standard. The UE determines whether thePCell RSRP is less than the S-Measure at step 1605. If the PCell RSRP isless than the S-Measure, the UE performs the intra-frequency,inter-frequency, and inter-RAT measurements at step 1610.

The UE also determines whether the SCell RSRP is less than theS-MeasureForSCell at step 1605. If the SCell RSRP is less than theS-MeasureForSCell, the UE performs at least intra-frequency measurementat step 1610. The UE may perform the inter-frequency and inter-RATmeasurements additionally.

If none of the two conditions is fulfilled at step 1605, the proceduregoes to step 1615. At step 1615, the UE performs only the cellmeasurement on the current serving cell.

If the cell measurement configuration information received through theRRC Connection Reconfiguration message does not include the S-Measureand S-MeasureForSCell, the procedure goes to step 1620. At step 1620,the UE determines whether the following two conditions are fulfilled.

The UE determines whether neither of the S-measure nor S-MeasureForSCellis received at step 1620 and, if none of the S-measure andS-MeasureForSCell is received, performs the intra-frequency measurementat step 1610. The UE also may perform the inter-frequency and inter-RATmeasurements additionally.

If only the S-Measure is received at step 1620 and if the dualconnectivity or carrier aggregation is configured, the procedure goes tostep 1610. At step 1610, the UE performs the intra-frequencymeasurement. The UE also may perform the inter-frequency and inter-RATmeasurements additionally.

If none of the two conditions is fulfilled at step 1620, the proceduregoes to step 1615. At step 1615, the UE performs only the cellmeasurement on the current serving cell.

FIG. 17 illustrates a block diagram of a configuration of the UEaccording to embodiments of the present disclosure. As shown in FIG. 17,the UE according to embodiments of the present disclosure includes atransceiver 1700, a multiplexer/demultiplexer 1705, an upper layerprocessor 1710, a control message processor 1715, and a controller 1720.In the case of transmitting control signals and/or data to the eNB, theUE multiplexes the controls signals and/or data by themultiplexer/demultiplexer 1705 and transmits the multiplexed signal byway of the transceiver 1700 under the control of the controller 1720. Inthe case of receiving signals, the UE receives a physical signal by thetransceiver 1700, demultiplexes the received signal by themultiplexer/demultiplexer 1705, and delivers the demultiplexedinformation to the higher layer processor 1710 and/or control messageprocessor 1715, under the control of the controller 1720.

The controller 1720 controls the overall operations of the UE. Accordingto embodiments of the present disclosure, the controller 1720 controlsthe UE to perform cell measurement and report cell measurementinformation to the macro eNB based on the cell measurement requestreceived from the macro eNB. The controller 1720 may control the UE toreceive the eNB configuration information including the indicatorindicating a specific cell of the small cell which is received from themacro eNB or the small cell eNB.

The controller 1720 also may control to transmit uplink control channelto the small cell eNB serving the UE through a specific cell indicatedby the indicator.

The controller 1720 also may control the UE operations described withreference to FIGS. 1 to 16.

Although the description is made in such a way that the UE is composedof a plurality function blocks responsible for different functions, theconfiguration of the UE is not limited thereto. For example, thefunctions of the multiplexer/demultiplexer 1705 may be performed by thecontroller 1720.

FIG. 18 illustrates a block diagram of a configuration of the eNBaccording to embodiments of the present disclosure. As shown in FIG. 18,the eNB includes a transceiver 1805, a controller 1810, amultiplexer/demultiplexer 1820, a control message processor 1835,various upper layer processors 1825 and 1830, and a scheduler 1815.

The transceiver 1805 transmits data and predetermined control signalsthrough a downlink channel. The transceiver 1805 receives data andpredetermined control signals through an uplink channel. In the casethat a plurality of carriers is configured, the transceiver 1805transmits and receives data and control signals through the pluralcarriers.

The multiplexer/demultiplexer 1820 is responsible for multiplexing datagenerated by the upper layer processors 1825 and 1830 and the controlmessage processor 1835 or demultiplexing data received by thetransceiver 1805 to deliver the demultiplexed data to the upper layerprocessors 1825 and 1830, the control message processor 1835, and thecontroller 1810. The control message processor 1835 processes thecontrol message transmitted by the UE to take a necessary action orgenerates a control message addressed to the UE to the lower layer.

The upper layer processor 1825 (or 1830) is established per UE or perservice to process the data generated in association with the userservice such as File Transfer Protocol (FTP) and Voice over InternetProtocol (VoIP) and transfer the processed data to themultiplexer/demultiplexer 1820 or process the data from themultiplexer/demultiplexer 1820 and transfer the processed data to theupper layer service applications.

The scheduler 1815 allocates transmission resource to the UE at anappropriate timing based on the buffer status, channel status, andActive Time of the UE and controls the transceiver 1805 to process thesignals received from and to be transmitted to the UE.

The controller 1810 determines the data transmission timing of the UEand controls the transceiver 1805 to receive data. The controller 1810controls the overall operations of the eNB. According to embodiments ofthe present disclosure, the controller 1810 controls the operations ofthe macro eNB. A description is made of the operation of the controllerof the macro eNB.

The controller 1810 receives the cell measurement information about theserving and neighboring cells from at least one UE served by the macroeNB. The controller 1810 receives the status information including theload information on the serving cells of the small cell eNB from thesmall cell eNB. The controller 1810 determines the Secondary Cell Group(SCG) of the serving cells of the small cell eNB that are capable ofserving the UE based on the cell measurement information and the statusinformation. The controller 1810 controls to transmit the SCGinformation to the small cell eNB. At this time, the SCG information canbe used when the small cell eNB selects a specific cell for PUCCHtransmission of the UE.

The controller 1810 also may control to configure a specific cellcandidate set with the cells of which signal strengths are equal to orgreater than a predetermined threshold among the serving cells includedin the SCG. The controller 1810 also may control to select the specificcell among the at least one cell included in the candidate set.

The controller 1810 may control to transmit the specific cell candidateset information to the small cell eNB for use in selecting the specificcell. If the SCG is identical with the candidate set, the controller1810 may control to do not transmit the candidate set information.

The controller 1810 also may control to receive the small cell eNBconfiguration information including an indicator indicating the specificcell from the small cell eNB and to transmit the configurationinformation including the indicator to the UE. At this time, theindicator may include one of the CellGlobalID, PhysCellId, SCellIndex,bit indication information, and bitmap information.

A description is made of the operation of the controller of the smallcell eNB. The controller 1810 may control the small cell eNB to receivethe information on the Secondary Cell Group (SCG) including the servingcells through which the small cell eNB is capable of serving the UE fromthe macro eNB and to select a specific cell for the UE to transmit PUCCHbased on the received SCG information.

The controller 1810 also may control the small cell eNB to determine thespecific cell based on the per-cell received reference signal strength,received reference signal quality and/or the cell measurement resultreceived from the UE.

The controller 1810 also may control the small cell eNB to receive theinformation on the candidate set composed of the cells of which signalstrengths are equal to or greater than a predetermined threshold valueamong the serving cells included in the SCG from the macro eNB and toselect the specific cell based on the received candidate setinformation. The controller 1810 also may control the small cell eNB totransmit the small cell eNB configuration information including theindicator indicating the selected specific cell to the macro eNB.

The controller 1810 also may control the overall eNB operationsdescribed with reference to FIGS. 1 to 16.

Although the present disclosure has been described with embodiments,various changes and modifications may be suggested to one skilled in theart. It is intended that the present disclosure encompass such changesand modifications as fall within the scope of the appended claims.

What is claimed is:
 1. A method by a master base station in a wirelesscommunication system, the method comprising: transmitting, to asecondary base station, a first message requesting establishment of asecondary cell group (SCG) of the secondary base station; receiving, inresponse to the transmission of the first message, a second messageincluding information on a SCG configuration from the secondary basestation, the information on the SCG configuration including informationon a primary secondary cell (PSCell) of the SCG; and transmitting aradio resource control (RRC) reconfiguration message including theinformation on the PSCell to a terminal.